1. Field of the Invention
The present invention relates to a hydrocarbon blend useful for dissolving asphaltenic residues and to the process for treating, with the above said blend, the oil wells in order to remove the asphaltenic deposits.
Crude oil is a complex mixture of paraffinic, cycloparaffinic and aromatic hydrocarbons, in which components are present which have a wide range of properties: in fact, the present species range from very fluid liquids to waxy solids and very high viscosity tars.
Among the solid, or very thick, components, the asphaltenes predominate. They consist of a variable-composition mixture of fused aromatic polycyclic compounds.
Owing to the presence of various metals and heteroatoms, such as oxygen, nitrogen and sulfur, asphaltenes are among most polar components of crude oil.
In crude oil the asphaltenic particles tend to form micelles, generally of spherical shape and having a diameter comprised within the range of from 30 to 60 .ANG.ngstroms, wherein the asphaltenes constitute the central core of said micelles.
Lighter aromatic compounds and polar products surround the core of the micelle, favouring the dissolution of asphaltenes in oil.
The recovery of crude oil contained in geological formations is often prevented the by presence of solid asphaltenic deposits. In fact, during the exploitation of an oil well, high molecular weight asphaltenic compounds can often precipitate together with waxy solids.
These solids tend to occlude the pores of the rocky reserve of oil, and, furthermore, to block well casings, pipes and further equipment used in borehole drilling. As a consequence, the productivity of well decreases and, in extreme cases, the total loss of well production occurs.
2. Description of the Related Art
Several useful methods are known for removing the above said solid deposits, e.g., mechanical scraping, hot oil treatment, treatment with aqueous surfactant solutions. However, the most widely used technique consists in using organic solvents capable of dissolving the above said asphaltenic deposits.
For that purpose, the generally used solvents are light aromatic species, e.g., benzene, toluene and xylene.
Besides their considerably high cost, the above said solvents display very serious drawbacks, deriving from their high volatility and their low flash point. Furthermore, the above said aromatic compositions are not completely satisfactory, owing to their poor capability of dissolving the asphaltenic residues, and to the rather low kinetics of dissolution thereof.